Get as close of a color match as possible. Paint your touchup area but take the extra on your brush and "dry brush" it in a large area, 8-12 inches, around your touchup so the paint kind of fades out to the dry wall. It'll hide your touchup much better.

If you take in a piece of paint or wall, at least the size of a quarter, they should be able to use their spectrometer to get a match.